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Subject[PATCH 22/73] union-mount: Add two superblock fields for union mounts [ver #2]
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From: Valerie Aurora <vaurora@redhat.com>

Add two fields to struct super_block to support union mounts:

(*) s_union_lower_mnts

A pointer to a cloned vfsmount tree of all the lower (read-only) mounts
unioned with the topmost (read-write) vfsmount. These mounts may have
submounts which will also be unioned; hence we copy the entire vfsmount
tree, not just the root vfsmounts.

(*) s_union_count

The number of lower mounts unioned at the root of the file system. This
count is the maximum number of directories that will ever be unioned with
a single directory. We use it to allocate a union stack of the correct
size for each directory.

Original-author: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---
include/linux/fs.h | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a014f0f..f19772c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1509,6 +1509,16 @@ struct super_block {
* free_vfsmnt() if MNT_HARD_READONLY is set.
*/
int s_hard_readonly_users;
+
+ /* Root of the private cloned vfsmount tree of the read-only
+ * mounts in this union (set in topmost vfsmount only)
+ */
+ struct vfsmount *s_union_lower_mnts;
+
+ /* Number of layers in this union, not counting the topmost or
+ * submounts.
+ */
+ unsigned int s_union_count;
};

/* superblock cache pruning functions */


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